A torque converter and a fluid coupling are classified as fluid type power transmission devices to be used in vehicles.
The torque converter has a function of transmitting power in conjunction with circulation of working fluid filled in the interior of the torque converter. Further, the torque converter has a function of amplifying torque in accordance with a speed ratio.
The torque converter is normally composed of three kinds of blade wheels (i.e., impeller, turbine and stator). The impeller is coupled to a crankshaft of an engine, for instance. The turbine is opposed to the impeller while being coupled to an input shaft of a transmission, for instance. The turbine is driven by the flow of fluid from the impeller thereto. The stator is interposed between the inner periphery of the impeller and that of the turbine, for instance. The stator is supported by a fixed shaft extended from the transmission through a one-way clutch, for instance.
The working fluid is supplied to the interior of the torque converter from a hydraulic circuit and is then discharged from it. For example, the working fluid is supplied from a space between an impeller hub and the fixed shaft, and enters the torque converter from a space between the impeller and the stator. The working fluid subsequently gets out of the torque converter from a space between the turbine and the stator. Subsequently, the working fluid is discharged from a space between the fixed shaft and a transmission input shaft. The working fluid is used as the lubrication oil for the transmission after being discharged from the torque converter (see, e.g., Japanese Laid-Open Patent Publication No. JP-A-H05-263895).
Just the same as the torque converter, the fluid coupling has a function of transmitting power in conjunction with circulation of the working fluid filled in the interior thereof. However, the fluid coupling is not provided with a stator. Accordingly, the fluid coupling does not have a function of amplifying torque.